This book is a great resource. I've gone back to it frequently. If you're interested in getting into statistics and machine learning, I cannot recommend this book highly enough. The motivations are good, and the explanations are good. Shalizi's class for this book at CMU is highly sought after, and some of that surely makes its way into this massive book.
Before taking this class I didn't know cross validation, bootstrapping or about double dipping data. I think those are the most important takeaways. The discussion of causality and building graphical models was good as well.
Elementary must be one of those words that does not exactly mean what you think.<p>The first formula (regression on page 29) instantly drops some math in there without any discussion of what it does or how it got there... :(